INTERPLANETARY DUST MAY CAUSE CLIMATE CHANGE, GRADUAL EXTINCTION

GAINESVILLE -- Space dust in the earth's atmosphere and changes in the
planet's orbit may have started the gradual extinction of dinosaurs and
other life thousands of years before a massive asteroid collision dealt the
final blow, according to research from the University of Florida and the
Carnegie Institution of Washington.

The dust build-up, which rises and falls on about a 100,000-year cycle, also
may answer some big questions researchers have about the history of earth's
climate, said Stanley Dermott, chairman of UF's astronomy department.

"A major, outstanding problem in present day geophysics is understanding the
history of earth's climate," said Dermott.

The research is published in the May 8, 1998 issue of the journal
Science.

The earth's climate varies on a 100,000 year scale, and during that time the
earth's eccentricity changes causing the earth to move closer or farther
away from the sun. Current scientific thinking says this variation in the
amount of sunlight reaching the earth, known as the Milankovich Effect,
changed the earth's climate.

But Dermott and Stephen Kortenkamp, a postdoctoral fellow at the Carnegie
Institution, both felt this assumption was unlikely.

"The amount of variation is extremely small," Dermott said.

Dermott and Kortenkamp did calculations spanning 1.2 million years to prove
the amount of dust in the atmosphere did vary and that the eccentricity of
Earth's orbit can make dust accumulation rates vary by a factor of 2 or 3.
Dermott said the earth gains nearly 30 million kilograms of dust a year, and
the amount of dust in the atmosphere could effect earth's climate.

However, Dermott said, even that amount of dust is relatively small, so
scientists still aren't sure exactly how much it could influence the
climate.

Earth accumulates dust through gravitational focusing, an effect that causes
the earth to pull dust particles toward it. To gather information on dust
levels, NASA launched a craft the size of a school bus into the earth's
atmosphere and counted the number of particle impacts on the side of the
craft over several years. "It was a good record of the impact of dust
striking earth," said Dermott.

Kortenkamp, a UF graduate, said the effects of interplanetary dust on the
climate will be similar to the effects of volcanic dust in the atmosphere.
Past volcanic eruptions have caused a detectable cooling of the earth's
surface. Volcanic dust settles in a couple of months and the cooling effect
is short-term.

But the effects of space dust on the atmosphere can last much longer. "The
influx of interplanetary dust could remain at high levels for extended
periods several hundred thousand years and therefore any associated cooling
would also persist for this length of time," said Kortenkamp.

The researchers also examined the possibility that if the amount of dust in
earth's atmosphere altered the climate, the change could cause gradual
extinctions.

Dermott said every 100 million years the majority life on earth is destroyed
by a catastrophic event, such as an asteroid striking Earth's surface, but
history doesn't show an exact moment or date in time for the extinction of
life.

Dermott and Kortenkamp are investigating the idea that if atmospheric dust
effects the climate, then the dust may effect life on earth as well. For
example, an asteroid collision creates a dust wave that reaches earth 1
million years before the asteroid. The dust may alter the climate enough to
cause a gradual extinction before the asteroid hits earth's surface and
causes a catastrophic event.

"While the issue is controversial, there are groups of paleontologists who
have found evidence suggesting some mass extinctions were gradual, lasting
for hundreds of thousands of years," Kortenkamp said.

To prove their theory, Kortenkamp said, a detailed analysis must be done of
geological records looking for enhanced dust accumulation connected with
gradual mass extinctions.